3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
It is important to properly regulate a transmit power when a user equipment (UE) transmits data to a base station (BS). If the transmit power is too low, the BS may not be able to correctly receive the data. If the transmit power is too high, it may cause interference to another UE. Therefore, the BS regulates the transmit power of the UE in a wireless communication system.
In order for the BS to regulate the transmit power of the UE, it is required to acquire essential information from the UE. A representative example thereof is a power headroom. The power headroom implies a power that can be further used in addition to the transmit power currently used by the UE. The power headroom may imply a difference between a maximum transmit power of the UE and the currently used transmit power.
When the BS receives the power headroom from the UE, the BS determines a transmit power to be used in next UE's uplink transmission on the basis of the power headroom. The determined transmit power is indicated by a resource block size and a modulation and coding scheme (MCS).
When a transmit power used by the BS in uplink scheduling is different from a transmit power that can be actually used by the UE, reliability of uplink transmission may deteriorate.